Recently, in line with portable, miniaturization, lightweight, and high-performance trends in electronic devices, electronics, information and telecommunications industries have rapidly grown. Accordingly, high-performance lithium secondary batteries are being used as power sources of these portable electronic devices, and the demand therefor is being rapidly increased. Secondary batteries, which can be repeatedly used by being charged and discharged, are essential for power sources of portable electronic devices for information and telecommunication, electric bikes, or electric vehicles.
In particular, since the performance of these products may depend on batteries as a key component, customer demand for high-capacity batteries is being increased. It is a trend that the development of a high-voltage battery system is performed according to the increase in the capacities of the batteries.
With respect to a typical lithium secondary battery, charge has been performed at a charge voltage of 3.0 V to 4.2 V. Thus, research into obtaining higher energy capacity is performed by using a charge voltage (4.3 V to 5.0 V) higher than the above voltage.
However, in a case where a non-aqueous carbonate-based solvent is used as an electrolyte solution together with an anode and a cathode which are typically used, since oxidizing power may be increased when charge is performed at a voltage higher than a typical charge potential of 4.2 V, the anode and the cathode may deteriorate and a decomposition reaction of the electrolyte solution proceeds as charge and discharge cycles are performed. Thus, lifetime characteristics may be rapidly decreased.
With respect to LiCoO2 as a typical cathode active material, since thermal and electrochemical properties thereof may be inappropriate when used at a high voltage, there is a need to improve the above limitations.